edit2: In fact, it is pretty clearly illustrated in the Penal Code that you must lock handguns for transport.

Ie. driving with a pistol on the passenger seat is going to get you a visit to the gray bar motel

only if it is concealed. If it is openly displayed on the passenger seat, it is not a violation of 12025.

Quote:

12025
(a) A person is guilty of carrying a concealed firearm when
he or she does any of the following:
(1) Carries concealed within any vehicle which is under his or her
control or direction any pistol, revolver, or other firearm capable
of being concealed upon the person.

he would have to make sure he didn't violate any GFSZ during he drive, but that wouldn't be a 12025 violation.